The Justice Department on Wednesday sued to block AT&T’s $39 billion pursuit of T-Mobile, saying the deal would leave consumers with fewer choices and higher bills for mobile phone service that has become “indispensable” to the way Americans live and do business.

AT&T immediately vowed to challenge the lawsuit, setting the stage for the most significant antitrust battle of the Obama administration, which had vowed to rigorously police big business deals that are bad for consumers. But Justice has rarely gone to court to stop blockbuster deals, and it failed the last time it sued to prevent a big corporate merger, seven years ago.

Justice officials said the outcome of the deal, which would combine the second- and fourth-largest wireless companies, made their decision clear.

“Unless this merger is blocked . . . consumers will suffer,” said Sharis A. Pozen, acting assistant attorney general in Justice’s Antitrust Division. “Any way you look at this transaction, it is anti-competitive.”

The Justice Department did battle with an earlier version of AT&T, famously breaking up “Ma Bell” in 1984. But since then, AT&T has reestablished itself as one the best-connected companies in Washington, armed with a massive lobbying operation.

Justice’s decision comes at a sensitive time for President Obama, who is launching his reelection campaign and facing complaints from businesses that his administration is getting in the way of efforts to spur economic growth and create jobs.

Deputy Attorney General James M. Cole said Wednesday that the department’s decision would actually “protect jobs in this economy.”

For months, AT&T has been arguing the opposite, saying the merger would put “tens of thousands” of people to work by bringing wireless high-speed Internet access to an additional 55 million Americans.

In a show of goodwill, AT&T senior executives on Tuesday met with Justice officials to tell them that they would bring 5,000 call-center jobs back to the United States from overseas. The executives got no hint that a day later Justice would file suit, according to a source familiar with the meeting.

“We are surprised and disappointed by today’s action,” AT&T General Counsel Wayne Watts said in a statement. He said the company would ask the U.S. District Court for the District of Columbia for an expedited hearing. “We remain confident that this merger is in the best interests of consumers and our country, and the facts will prevail in court.”

AT&T has a lot to lose. If the merger does not conclude by September 2012, the company will have to hand over $3 billion worth of wireless spectrum and other assets to T-Mobile’s parent company, Deutsche Telekom. AT&T would also have to pay $3 billion in cash, which would be the largest breakup fee in history, according to Thomson Reuters.

AT&T’s stock dropped 3.8 percent, to $28.48, on Wednesday. Shares of Sprint Nextel, the nation’s third-largest carrier, rose 5.9 percent, to $3.76. Sprint had warned that its business couldn’t survive if the merger was approved, and it had been interested in buying T-Mobile before AT&T’s bid.

Apart from Justice, government regulators reviewing the deal expressed skepticism that it would be good for consumers.

“Competition is an essential component of the FCC’s statutory public interest analysis . . . and although our process is not complete, the record before this agency also raises serious concerns about the impact of the proposed transaction on competition,” Julius Genachowski, chairman of the Federal Communications Commission, said Wednesday, in his strongest criticism of the deal to date.

The FCC has not made a decision. But an FCC official, commenting on the condition of anonymity because the review is ongoing, said: “We will not undermine the DOJ’s process. You read the tea leaves from that.”

The courts have not always been kind to Justice when it brings antitrust cases.

The AT&T merger will go before U.S. District Judge Ellen Huvelle, who in 2001 ruled against the department’s effort to block SunGard Data Systems’ acquisition of Comdisco. In a better-known case, U.S. District Judge Vaughn R. Walker in 2004 turned down Justice’s request to block Oracle’s $10 billion acquisition of PeopleSoft.

In most cases, Justice tries to get companies to walk away from mergers by threatening legal action rather than going to court. Under Obama, the department has mostly greenlighted big mergers, even the most controversial ones, although it has attached conditions to the deals.

Some analysts said it is still possible for AT&T and Justice to arrive at a settlement.

“In light of the government’s mixed record in merger litigation, the political sensitivities associated with the deal in advance of the 2012 presidential-election year . . . negotiation . . . may yet result in a settlement down the road,” said Jeff Silva, an analyst at Global Medley Advisors.

But for now, Justice officials do not see a remedy that would solve the problem of having more than 80 percent of all U.S. wireless customers in the hands of two players, AT&T and Verizon Wireless, according to a source familiar with Justice’s thinking.

Pozen, the acting assistant attorney general, said the agency will work with AT&T to resolve antitrust concerns.

“Our door is open,” she said, signaling the possibility that the deal could succeed through a settlement out of court. “We’ll see what happens next,” she said.

Consumer groups applauded Justice’s action.

T-Mobile is viewed as a low-cost alternative to AT&T and Verizon Wireless. Consumers Union, the publisher of Consumer Reports, found that T-Mobile’s data plan is on average 50 percent cheaper than AT&T’s.

Other consumer advocacy groups said AT&T has eliminated unlimited data plans for customers and raised prices on some service plans even as consumers increasingly rely on their phones to make calls and gain access to the Internet. One in four American households has abandoned traditional telephone lines and relies solely on mobile devices.

“We are delighted that law has trumped politics and that the DOJ looked at facts and decided the merger is bad for competition and consumers,” said Gigi Sohn, president of the public interest group Public Knowledge.

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